One example of materials hard to cut in the cutting process is a Ni-base heat-resistant alloy. When a cemented carbide tool that has been frequently used in the cutting process of a Ni-base heat-resistant alloy, serving as a workpiece, is used, the cutting speed is restricted to 80 m/min or lower at the fastest in consideration of the strength of the tool, whereby enhancement of the work efficiency is prevented.
Thus, it has been studied to perform cutting at a high speed of 200 m/min or higher using a cubic boron nitride cutting tool including a cutting edge made of a sintered cubic boron nitride compact that has a high hot hardness.
While cubic boron nitride has a higher hardness than cemented carbide, cubic boron nitride has a low toughness. Thus, a lateral cutting edge portion is chipped when the above-described cubic boron nitride cutting tool is used to cut a heat-resistant alloy and the cubic boron nitride cutting tool is insufficient for reliable life sustainability. Although cubic boron nitride has a higher toughness than ceramics, the lack of toughness for cutting a heat-resistant alloy is undeniable.
As illustrated in PTL 1 below, a trial conducted as a measure to address the above problem is to cut a workpiece while the workpiece is softened with the heat (cutting heat) occurring at the edge formed of the sintered cubic boron nitride compact as a result of reduction of the thermal conductivity of the sintered cubic boron nitride compact.
Another measure to toughen the cutting edge is to make the rake angle at the edge negative by forming a negative rake face or by other means. This measure is effective in preventing chipping of a cutting edge made of a brittle material.